Generally, conductive vias are used in integrated circuits to provide electrical connection between a conductor on a first layer and a conductor on a second layer that is above the first layer, where there is a dielectric layer between the first and second layers. The formation of vias typically involves etching through the intervening dielectric layer prior to the deposition of the second layer, and then removing the mask used in the etching process. The etching and mask removal steps typically leave a residue in the bottom of the via cavity, which residue reduces the conductivity of the via if not adequately removed or otherwise accounted for. Physical sputtering processes are often used to remove such residue from the bottom of via cavities. However, sputtering also causes removal of some of the dielectric material, such as from the walls of the via cavity, and tends to redeposit the dielectric debris in the bottom of the via cavity. Such debris also tends to reduce the conductivity of the via.
Formation of vias also typically involves depositing a liner material, such as titanium nitride, on the bottom and sides of the via cavity prior to depositing a via metal. The liner material tends to reduce electromigration of the via metal, and protects materials adjacent the via from reaction with gases used in the formation of the via metal. Liner materials deposited by chemical vapor deposition tend to be porous. If the liner material is too porous, it is less effective in performing the liner functions described above. Prior methods of reducing porosity of the liner material tend to be inadequate, especially on the sidewalls of the via cavity.
What is needed, therefore, is a more effective process for reducing the porosity of a liner material in a via cavity. A process is also needed for effectively removing residue from the bottom of a via prior to depositing the via metal.